Benzene-derived N-(4-hydroxyphenyl)-deoxyguanosine adduct: UvrABC incision and its conformation in DNA

Benzene, a ubiquitous human carcinogen, forms DNA adducts through its metabolites such as p-benzoquinone (p-BQ) and hydroquinone (HQ). N²-(4-Hydroxyphenyl)-2′-deoxyguanosine (N²-4-HOPh-dG) is the principal adduct identified in vivo by ³²P-postlabeling in cells or animals treated with p-BQ or HQ. To study its effect on repair specificity and replication fidelity, we recently synthesized defined oligonucleotides containing a site-specific adduct using phosphoramidite chemistry. We here report the repair of this adduct by Escherichia coli UvrABC complex, which performs the initial damage recognition and incision steps in the nucleotide excision repair (NER) pathway. We first showed that the p-BQ-treated plasmid was efficiently cleaved by the complex, indicating the formation of DNA lesions that are substrates for NER. Using a 40-mer substrate, we found that UvrABC incises the DNA strand containing N²-4-HOPh-dG in a dose- and time-dependent manner. The specificity of such repair was also compared with that of DNA glycosylases and damage-specific endonucleases of E. coli, both of which were found to have no detectable activity toward N²-4-HOPh-dG. To understand why this adduct is specifically recognized and processed by UvrABC, molecular modeling studies were performed. Analysis of molecular dynamics trajectories showed that stable G:C-like hydrogen bonding patterns of all three Watson–Crick hydrogen bonds are present within the N²-4-HOPh-G:C base pair, with the hydroxyphenyl ring at an almost planar position. In addition, N²-4-HOPh-dG has a tendency to form more stable stacking interactions than a normal G in B-type DNA. These conformational properties may be critical in differential recognition of this adduct by specific repair enzymes.     

Pediatric convulsive status epilepticus in Honduras, Central America

Convulsive status epilepticus (SE) in children is an important public health problem, particularly in low-resource countries. A surveillance study was performed with consecutive enrollment of all children presenting with convulsive SE to Hospital Escuela Materno-Infantil Emergency Department in Tegucigalpa, Honduras over a 13-week period in 2003. In the 47 children with SE, the mean age was 4.5 years and the median seizure duration was 95 min. Mortality and morbidity were higher in children from rural locations, with all six deaths and three cases of new neurologic abnormalities occurring in rural children who had acute symptomatic SE. We conclude that childhood SE is common in the low-resource developing country of Honduras. Given the long delays in obtaining initial treatment in pediatric emergency facilities, availability of prehospital treatment may be of particular importance in this setting.     

Blood vessels form a migratory scaffold in the rostral migratory stream

In adult mice, new neurons born in the subventricular zone (SVZ), lining the lateral ventricles, migrate tangentially into the olfactory bulb along a well‐delineated path, the rostral migratory stream (RMS). Neuroblasts in the RMS migrate tangentially in chains, without a recognized migratory scaffold. Here we quantitatively examine the distribution of, and relationships between, cells within the RMS, throughout its rostral‐caudal extent. We show that there is a higher density of blood vessels in the RMS than in other brain regions, including areas with equal cell density, and that the orientation of blood vessels parallels the RMS throughout the caudal to rostral path. Of particular interest, migratory neuroblast chains are longitudinally aligned along blood vessels within the RMS, with over 80% of vessel length in rostral areas of the RMS apposed by neuroblasts. Electron micrographs show direct contact between endothelial cells and neuroblasts, although intervening astrocytic processes are often present. Within the RMS, astrocytes arborize extensively, extending long processes that are parallel to blood vessels and the direction of neuroblast migration. Thus, the astrocytic processes establish a longitudinal alignment within the RMS, rather than a more typical stellate shape. This complementary alignment suggests that blood vessels and astrocytes may cooperatively establish a scaffold for migrating neuroblasts, as well as provide and regulate migratory cues. J. Comp. Neurol. 513:94–104, 2009. © 2009 Wiley‐Liss, Inc.